Fractionating apparatus



Feb. 20, 1962 M. H. KoTzEBUE 3,022,054

FRACTIONATING APPARATUS Filed Nov. 4, 1958 3 Sheets-Sheet 1 BY AATTORNEY Feb. 20, 1962 M. H. Korzx-:BUE

FRACTIONATING APPARATUS 3 Sheets-Sheet 2 Filed Nov. 4, 1958 llv 17?/ miif /We//ia/a/ /fa fzeae INVENTOR.

Feb. 20, 1962 M. H. KorzEBUE FRACTIONATING APPARATUS 3 Sheets-Sheet 5Filed Nov. 4, 1958 OO OOoo 0000090 OOOO MeV/7b O/a/ f7. /fo zeae IN VENTOR.

United States Patent O 3,022,054 FRACTIGNATING APPARATUS Meinhard H.Kotzebue, Houston, Tex., assigner to Gasoline Plant ConstructionCorporation, a Texas corporation Filed Nov. 4, 1953, Ser. No. 771,895 2Claims. (Cl. 261--114) This invention is a continuation-impart of myco-pending application, Serial No. 630,364, filed December 24, 1956, nowabandoned.

This invention relates -to fractionating apparatus and particularly totray constructions and arrangements for fractionating columns of thekind in which liquids and vapors are caused to counterilow to obtainintimate contact therebetween.

Fractionating columns having tray constructions and arrangements inaccordance with lthe present invention, while useful in manyv industriesrequiring such apparatus, are particularly useful for fractionation ofpetroleum hydrocarbons and more especially for the fractionation oflarge volumes of material comprising close-boiling fractions to effecthighly eicient separation of desired constituents having a high degreeof purity.

In the separation of close-boiling hydrocarbons as, for

example, isobutane from normal butane, isopentane from t normal pentane,cyclohexane from a crude fraction thereof, and ythe like, conventionalfractionating devices, such as the well-known bubble-cap trays, arerelatively inefcient, requiring large columns employing l0() trays ormore to etect separation of a desired product which will usually notexceed 95% in purity, particularly in plant scale operations handlinglarge volumes of material.

The present invention has for its primary objects the provision of animproved fractionating tower or column having novel tray constructionand arrangement by which large volume plant scale separations may beeffected be- `tween very close boiling constituents of a hydrocarbonmixture at fractionating eiiiciencies approaching 100% with theproduction of desired products having a degree of purity which is'practicably unattainableby present plant vscale systems, as for example99% purity. In particular, the present invention is especiallyapplicable to fclose' fractionation ofsuch large volumes of stocks asrequire coi- .tunns six to eight feet in diameter and larger.

A further object is the provision of a fractionating tower havingsubstantially higher eiciency and greater capacity than a moreconventional type fractioning tower ofthe same height and diameter.

An important object is the provision of a tray construction andarrangement by which the hydraulic gradient for the liquid owing acrossthe trays will be a minimum and maximum utilization of the towercross-section is made for reduction of entrainment and improvedfractionating etiiciency.

In accordance with the present invention the foregoing and other objectsof this invention may be attained by the employment of a trayarrangement having concentric circular downcomers, the downcomer of onetray being a generally cylindrical tube located in the center of thetray and the next adjacent tray having an annular downcomer disposedabout its periphery.` This alternating concentric downcomer arrangementcauses the liquid to travel across the tray surfaces along radial pathsat all points between the downcomers. ri`he liquid Will thus beuniformly distributed over the tray surfaces and all portions of ytheliquid will travel minimum distances between the downcomers to therebyreduce the hydraulic gradient of the trays. The vapor passages are of asuitable 'shape and 'are distributed uniformly through the area of theannular sections of the trays defined between the perimeters of ice thecircular downcomers, and are so constructed and arranged that maximumutilization of the entire crosssectional area of the vapor space betweenthe trays will be attained.

' More specifically the vapor passages are so shaped and arranged as toprovide increased vapor velocity adjacent the areas occupied by therespective downcomers whereby to direct vapor flow into and through thevapor spaces in the areas overlying the downcomers which, in moreconventional constructions, do not enter effectively into thefractionation operation.

A more specific object, therefore, is to provide a tray arrangementhaving the alternating concentric, central and peripheral downcomers,and gas passages through the trays increasing in orifice area radiallytoward the peripheries of the respective downcomers. That is, on a trayhaving the single central downcomer, the gas passage area will beincreased from the outer periphery of the tray toward the centraldowncomer, whereas on a tray having the annular peripheral downcomer thegas passage area will increase radially toward the peripheral downcomer.The result is to produce a vapor velocity gradient in the vapor spacesbetween the trays, which gradient increases radially in the direction ofthe respective downcomers.

" VOther and more specific objects and advantages of this invention-will become more readily apparent from the following description whenread in conjunction with the accompanying vdrawing which illustratesuseful embodiments in accordance with--this invention.

In the drawing:

FIG. 1 is a generally elevational view of a fractionating tower orcolumn in accordance with the present invention, the tray arrangementbeing illustrated diagrammatically in broken lines;

FIG. 2 is a fragmentary cross-sectional view of the tower illustratingone embodiment of the tray construction and arrangement in greaterdetail;

FIG. 3 is a partial plan view along line 3 3 of FIG. 2 of one of thetrays in accordance with the embodiment of FIG. 2;

FIG. 4 is an enlarged fragmentary longitudinal sectional view along line4 4 of FIG. 3 showing details of one of the vapor passages and itscontrol elements;

FIG. 5 is a cross-sectional View along line 5 5 of FIG. 4;

FIG. 6 is a view similar to FIG. 2 illustrating another embodiment ofthis invention including a tray modiiication employing a dilferent formof the vapor passages through the tray; and Y FIGS. 7 and 8 are partialplan views along lines 7 7 and 8 8, respectively, of FIG. 6 illustratingthe vapor passage arrangements of two of the trays illustrated 'u1 FIG.6.

Referring to FIG. l, there is shown a fractionating column or tower,designated generally by the numeral 10, comprising the cylindrical shellil having the bumped top and bottom heads l2, 13, respectively, andvertically disposed on a supporting skirt 14. Shell 11 is provided withthe usual vapor outlet nozzle l5 in top head i2 and liquid draw-offnozzle 16 near fthe lower portion ol' the tower. Circulating connections17 and 18 for a reboiler, heater, stripper, or the like (not shown) arevprovided in the lower portion of the .column in a generallyconventional arrangement for such connections. The column is alsoprovided with one or more of the usual feed nozzles 1,9 19 appropriatelyspaced along an intermediate portion thereof and near its upper portionwith a reflux feed nozzle 20.

Internally the tower is tted with a plurality of vertically spaced,horizontally disposed trays having two struc- .trallydiiferent butcooperable forms which alternate witheachg other throughout the tower,the two forms of trays being'designated generally by the respectivenumer- Vals 21a and 2lb and shown in greater detail in FIGS.

in the center thereof with a single relatively large diameter circulardowncomer 22 Vand about its outer periphery with an annular depressionforming the vapor-seal well 23 on the shell'side of the tray. The trayis supportably secured in fluid-tight engagement with Shell 11 aboutits'outer periphery in any suitable manner as by means of the anglebracket 24. A circular weir 25 is provided to extend above the uppersurface of the tray about the upper end of the downcomer and, as shown,may be formed by projecting the upper'end of the downcomer about thetray surface to a height to provide the desired level of liquid on thetray. Downcomer 22 extends below tray 21a a distance such that its lowerend will extend tray 21a, preferably in ywell 23 with which downcomerwardly and inwardly to provide the frusto-conical shape illustrated butit will be understood that downcomer 22V may be cylindrical throughoutits length. The portion of tray 21a defined between the perimeters ofdown-` comer `22 and well 23 constitutes the annular'ioor secwill be insubstantial concentric alignment.

Wall 31 may be tapered downwardly and outwardly to have reduced width atits lower end as shown. At its center tray 2lb may be provided with acircular vaporseal well 33 underlying the lower end of downcomer 22, andwell 33 may be'provided with a removable bottom 34 whereby to provideaccess man-ways through trays 2lb. The portionV of tray 2lb definedbetween the perimeters of downcomer wall V31 and well 33 constitutes theannular oor section 26a 'which will have substantially the same radialwidth as oor section 26 of tray 21a. Floor section 26a will also bepierced by vapor passages 27 having the identical form and arrangementas those in tray 21a and being provided with identical control strips 28and guides 29. Trays 2lb may be supported from the tower shell or fromtrays 21a in any suitable andconventional manner, well understood'bythose skilled in this art, to maintain the desired spacing between thetrays. Y

The operation of the tower is as follows: Liquid,

' whether reflux to the top trayY or feed to one or more o f theintermediate trays, will ilow radially inwardly across tion 26 which ispierced by a multiplicity of vapor pas- Y sages 27.

row'elongate slots which extend radially throughout theY area of annulartloor section 26 to points closely adjacent the perimeters of downcomer2,2 and well 23. The an? guiar spacing between the slots is madesubstantially equal to provide uniformity in the distribution ofthervaporliquid contacts on the tray.

As best seen in FIGS. V4 and V5, slots 27 are preferably provided withthe control strips 28 which function as check-valving elements for theslots and comprise the elongate flat strips, which may be constructed ofsheet metal or other suitable rigid material, which -register with andoverlie the vapor slots 27. Upward movement of control strips 28 islimited by means of a plurality -of Ylongitudinally spaced keeper guides29'of inverted U- the tray surface, for example, tray 21a, from theshell side at which it is introduced and will overow weir 25 and ilowthrough downcomer 22 into well 33 Yof the next lower tray 2lb. From well33 the liquid will ow radially out.- wardly across the tray to thershellside of the tray and pass over weir 32 yinto downcomer 30 which willdeliver the liquid into annular well 23 of the next lower tray 21u,

Y, whence the liquid will again'ow `radially inwardly to the centraldowncomer of the latter tray, this radial in and Y out ow being repeatedas the liquid flows downwardly shape, the legs of which are secured tothe tray surface and the tray floor will increase uniformly radiallyofthe tray, theV greater orifice area being at the ends of the con-'trol strips adjacent the traydowncomer. Y t

Tray 2lb is also off generally circular shape somewhat smaller in'diameter than shell 171'to provide an annularV downcomer 30 Yabout thetray periphery, downcomer 30 being `,delined on its Youter side byshellll Vand on the 'inner side bythe circular wall 31 secured to theouter periphery of the tray. A circular weir'32 is provided to Vextendabove the upper surface Yof tray 2lb about the upper end of .downcomer30 and, as shown, may be ormed by projecting theupper'endV of wall 31above the traysurface toga height to 'provide vthe desired level of.distance such that its lower end `willgextend beneath the ysurface Vofliquid which is maintained on the next lower vwhich increases radiallyinthe direction of the respective V ,liquidson tray l2117. Wallllextends below 1trayf:21b:a

throughout the entire series of trays. The solid arrows in FIG. 2designate the path of ow of the'liquid across the trays. Y

l The radial movement of liquid between the concentric downcomersprovides a maximum degree of uniformity in the distribution of thedownowing liquid over the tray surfaces; reduces the danger ofchanneling to an absolute minimum; and the radial ow provides theminimum hydraulic gradient for the trays. 'Y Y The vapor ilowingupwardly throughthe tower from tray to tray, `along paths indicatedbythe broken line arrows in FIG.Y2, will pass upwardly through vaporpassages 27 and will pass through the bodies of Yliquid maintained oneach tray by the Weirs 25 and'32.Y The ,depth of liquid maintained ontrays 21a and 21b,;respectively, will be greater than the maximum heightto which control strips 28 are permitted to raiseso that'the vaporpassages will always be coveredby'liquid. The vapor owing through thevapor passages will raise the control strips and will bubble throughthe'liquid bodies.

n .In order, however, to assure maximum fractionating' eiliciency kforthe column, it is important that .the maxii mum cross-sectional `area.of the vapor spaces be utilized. This requires Athat the otherwise dead`areas overlying the areas occupied'by the respective downoomers shouldbe occupied by upwardly ilowing vapor distribntedthere- '1n in aboutYthe same concentration ,as throughout the remainder of the vaporspaces, in orderthat these spaces may be employed -to reduce entrainmentof liquid in the vapors. Vdesirable result is obtained in'accordancewith this invention by the employment of .vapor passage means which willproduceV a velocity gradient inthe vapors downcomers, that is, towardthe areas of the vapor spaces overlying the downcomers on the'respectivetrays. Thus, as illustrated in FIGS.,2 to 5,' in'thecase ofA trays Zia'having the central downcomers V22, guides 29;will be varranged VtoVallow the ends of control Strips 28 Y,adjacent downcomers 22 to' raiseto a somewhat higher elevation 'above the tray licor than the oppositeiends of these con= trol strips lnearestthe SheIIside'QLtrays 21a.Cn'the other ranged to permit greatest elevation of the ends of controlstrips 28 nearest downcomers 30. The larger orificial areas thusprovided adjacent the respective downcomers will allow the vapors toflow at greater velocities through these larger orifices and therebycause the discharging vapors to spread radially and substantiallyuniformly throughout the vapor spaces overlying the respective downcomerareas. The broken arrowed lines in FIGS. 1 and 2 illustrate the generalpath of flow of the vapors through these spaces resulting from the vaporpassage control arrangements heretofore described. It will be noted thatthey indicate the vapor flow as being deflected laterally and, ofcourse, conccntrically of the vapor spaces through the areas overlyingthe downcomers.

The areas of the orifices defined between the side edges of the controlstrips and the tray floors is preferably made to increase substantiallyuniform radially of the floor sections of the trays, by employing theuniformly sloping arrangement of the control strips, as illustrated.However, it will be understood that other shapes for the gas dischargeorifices may be employed which, while not necessarily increasinguniformly in the radial direction, will, nevertheless, provide thedesired increased vapor velocity adjacent the downcomer areas.

It will be understood, of course, that the dimensions of the vapororifices will vary with the size and capacity of the fractionating towerin which they are to be employed. By way of example, in an eight-footdiameter tower, the control strips may be permitted to rise to a heightof 3A inch above tray floor sections at their higher ends and to aboutMs inch at their lower ends.

The uniform angular distribution of the vapor passages, as described,throughout the annular tray sections 26 and 26a, in combination with theuniform radial flow of liquid across the trays, produces maximumuniformity of distribution of the vapor-liquid contacts. This, togetherwith the described arrangement for increasing the vapor velocityadjacent the downcomer areas, provides superior scrubbing, heat exchangeefficiency, reduced entrainment, and other advantageous relationsbetween the vapor and liquid as to produce exceptionally highfractionation efficiency, particularly in large diameter columnshandling large volumes of hydrocarbons.

The greatly improved eiiiciency provided by the described trayarrangement and construction enables the separation of constituents ofas much as 99% purity from other constituents boiling within only 1 F.of the desired constituent. Moreover, such close eicient fractionationcan be attained when fractionating large volumes of material. Thisinvention is especially useful for large capacity towers, that is,towers more than six feet in diameter.

Fractionation efficiencies closely approaching 100% may be obtained withthe tray arrangement of this invention as compared with theapproximately 50% efficiency of bubble-cap trays or other moreconventional liquidvapor contactors, particularly in high capacityinstallations.

FIGS. 6, 7 and 8 illustrate another embodiment of this invention bywhich to obtain the desired increased vapor velocity through the trayareas adjacent the respective downcomers. In this embodiment, the vaporpassages are in the form of small perforations 27b arranged in radialrows extending across oor sections 26 and 26a, the rows being spacedapart at uniform angles. The perforations in each row are increased indiameter substantially uniformly in the direction of the downcomers onthe respective trays. In the case of trays 21a, the larger diameterperforations will be adjacent central downcomer 22, and

in the case of tray 2lb, the larger perforations will be nearest theshell side downcomers 30, as illustrated in FIGS. 7 and 8, respectively.In the case of an eight-foot tower, as in the example previouslymentioned, the diameters of the perforations will preferably varyuniformly from about 3A; inch to about 5e inch. This embodimentemploying the tray perforations is particularly useful in operationshaving a continuously maintained high vapor velocity, such as willprevent run-back of liquid through the perforations.

The dimensions of the. trays and downcomers, and the tray spacing, aswell as the design of the vapor passages will be determined inaccordance with well-known principles of tower design in relation to thetower sizes, capacities, the feed compositions and the products desired.

It will be understood that numerous changes and modifications may bemade in the details of the illustrative embodiments within the scope ofthe appended claims without departing from the spirit of this invention.

What I claim and desire to secure by Letters Patent is:

1. In a fractionating apparatus including a vertically disposedcylindrical shell, a fractionating tray arrangement for said shell,comprising, a plurality of vertically spaced, horizontally disposedcircular trays, alternate ones of said trays having single centrallylocated circular downcomers, and the intervening trays having continuousannular downcomers about their outer peripheries, the resultingconcentric relation of said downcomers cooperating to cause uniformlydistributed radial liow of liquid across the tray surfaces between thedowncomers, and vapor passage means substantially uniformly distributedthrough the annular sections of the trays defined between saiddowncomers, said Vapor passage means comprising a plurality of narrowelongate slots extending radially across said annular sections, a narrowelongate closure plate overlying each of said slots and movablevertically relative thereto for opening and closing said slots, andlimit means for said plates permitting a greater degree of upwardmovement of the ends of said plates adjacent the upper ends of saiddowncomers than of the opposite ends of the plates.

2. A fractionating column, comprising, a vertically disposed cylindricalshell having feed inlets and vapor and liquid outlets, a plurality ofvertically spaced horizontally disposed circular trays mounted in theshell, alternate ones of said trays having single centrally locatedcircular downcomers, and the intervening trays having continuous annulardowncomers about their outer peripheries, circular weirs about the upperends of the downcomers, the resulting concentric relation of said weirsand said downcomers cooperating to cause uniformly distributed radialflow of liquid across the tray surfaces between the downcomers, and amultiplicity of vapor passage means distributed substantially uniformlythroughout the areas of the annular sections of said trays definedbetween said downcomers, said vapor passage means comprising narrowelongate slots equi-angularly spaced extending radially across saidannular sections, a narrow elongate closure plate overlying each of saidslots and movable vertically relative thereto for opening and closingthe slots in response to the pressure of vapor flowing upwardly throughthe slots, and limit means for said plates permitting a greater degreeof upward movement of the ends of said plates adjacent the upper ends ofsaid downcomers than of the opposite ends of said plates.

References Cited in the file of this patent UNITED STATES PATENTS2,570,215 Dice Oct. 9, 1951 2,672,330 Swenson Mar. 16, 1954 2,718,900Nutter Sept. 27, 1955 2,747,849 Colburn et al May 29, 1956 2,772,080Huggins et al Nov. 27, 1956 2,809,821 Constantikes Oct. 15, 19572,810,562 Eid et al Oct. 22, 1957 2,973,189 Chu Feb. 28, 1961 FOREIGNPATENTS 518,215 Belgium Mar. 31, 1953 641,814 Germany Feb. 13, 19371,046,409 France July 8, 1953

